These books are gems, and I recall spending many weeks of co-ordination to get these books and a trip with my family and my mother to Sivananda at San Francisco, to get these books (one is on Kundalini).
People sometimes get turned off by the very mention of the words like "chakaras" and "naadis", and when they see the Kundalini Sign, the think of all this as some hocus-pocus stuff.
Every idea to be communicated needs some lexicon, some lexi-graphy, some archetype concept, and these symbols are from very ancient times, which we are not used to. If you do not believe me, try reading Ostrogodsky Theorem, which is nothing but Green's Theorem, published by MIR Publishers, Moscow (I read it when I was going to IIT). Or read Vector Calculus of 19th Century, and you would be lost and confused, thought the concepts are the same, and you may have already mastered the field. The issue is about what the brain is used to to in associating and parsing the symbols to derive the context and meaning. So these symbols are very scientific and reflect the same patterns found in 2D and 3D Standing Harmonics. Speak about the scientific know-how of the Ancients!
Modern Science is still playing catch up and just watch the videos on the "Chis". Places like MIT have only recently found the "magic of surprises" associated with this phenomenon. Just the think what a Vortex river can do to a swimmer and what Tornado Vortex does!
Chakras are nothing but the Energy Centres where we have the Medical Nervous Plexuses (where the afferent and efferent nerves meet - enter and exit like the planes in the Airport Hubbs, when one flies from Point A to Point B). The only difference is that the Plexusus one can see but Chakaras one can not see - Only advanced Yogis can feel sometimes their Energy Centers and can direct them, and very few advanced Masters can direct this to others and see and feel this Bio Energy. This is kind of a fundamental EMF energy, and I have seen a Yogi lighting a small LED Bulb at will.
Naadis are nothing but the same concept that run behind the nerves - as Energy Channels. Acu Pressure, Acu Puncture, Mar-mara of Ayurveda and Kaalri are having the same principle.
The Spiral (snake) Coils and the Main Shaft in the Kundaalni Symbol is nothing but the same symbol used by Modern Medicine. It is also the same symbol which was worshiped by the Ancients as Tree of Life and Shivalingam (Obelisk) Principle.
Only now the modern science is catching up. Beautiful things happen in Vortex point of Singularity - Big Bang, Black Hole, Super Conductivity, Embryo Formation, and so on. There are two coils to show the Downward Spiral Vortex ( broad to smaller spirals, from top to down) and the Upwards Spiral Vortex, (from big to small spiral from bottom to top). They symbolize the Positive and Negative Energy Fields, Heat and Cold, Male and Female Energies, or Prana and Apna.
The 7 Chakras correspond to the 7 Scales of the Mystery of the Harmonics, which is used everywhere - 7 Notes, 7 Days, 7 Planets, 7 Seers, and so on.